Shoe innersoles are employed with articles of footwear for a variety of purposes, such as to provide comfort, distribution of weight, arch or heel support and insulating qualities. Innersoles may be employed in athletic, jogging or running shoes and in general footwear, as well as in boots, such as mountain, hiking and cross-country boots, and in other footwear.
An innersole for an athletic shoe is described, for example, in U.S. Pat. No. 4,187,621, wherein the innersole comprises a laminate of two layers which is cut and conformed in contour to the last shape of the shoe, and which has an upper layer and a lower layer of different and defined compression sets. Typically, both of the upper and lower layers comprise cross-linked, closed-cell polyethylene polymers of different densities. However, it has been found that the polyethylene foam employed in such innersoles is not wholly satisfactory, since the polyethylene foam tends to break down in use, due to the poor compression set of the polyethylene foam, with a considerable reduction in cushioning, particularly in the heel section and the ball section of the foot, which tends to reduce cushioning to unsatisfactory comfort levels. Also, this laminate, while permitting the two-layer foam material to conform to the shape of the wearer's foot, does not provide adequate breathing properties.
Various polymers, including polyurethane foam materials, have been suggested for use in innersoles. For example, U.S. Pat. No. 3,781,231, issued Dec. 25, 1973, describes a resilient, cross-linked, hydrophilic, open-cell, polymer foam material which may be used to cast foams of varying thickness, and the innersoles may be cut to shoe-sole shape from sheets of the cast foam. Other shoe innersoles have been prepared having a laminated construction, such as described in U.S. Pat. No. 3,730,169, wherein a laminated cushion innersole is described as comprising an upper layer of generally smooth, low-friction material, the bottom layer of a generally resilient material, and an intermediate, permanently deformed cushion layer comprising an open-cell, polyurethane foam material. The innersole requires three separate layers of flat sheet material, with the object being to have the innersole deformed permanently on wearing, to conform the innersole to the shape of the wearer's foot; that is, to prepare a self-shaping innersole. The polyurethane material provides for plastic deformation to conform to the foot shape, while the bottom layer is adhesively secured to form a nonskidding layer.
Other flat-type, multiple-layer, inersole materials are described, for example, in U.S. Pat. No. 4,055,699, which innersole requires a dense, cross-linked polyolefin layer and an aluminum-coated moisture barrier layer, to provide insulation to the foot of the wearer. A protective insert for a shoe is also described in U.S. Pat. No. 3,638,336, wherein a foam closed-cell layer is laminated to a face layer of fabric, with the insert being contoured to conform to the innersole of the shoe, and having a sculptured heel portion to cup the heel of the wearer in use. Another innersole designed for heat insulation is described in British specification No. 1,243,575, wherein a flexible backing of leather or synthetic plastic material is secured to a heat-insulating layer of expandable polyethylene.
While prior innersoles, for use in articles of footwear, have been satisfactory generally for certain specific purposes, there are disadvantages associated with such innersoles, such as the breaking down of the foam layer with closed-cell, polyethylene-type innersoles, and the problems associated with the cost of laminating, forming and manufacturing the other innersoles. Therefore, there is a need for an improved innersole material and method of manufacture, which provides additional advantages and overcomes at least some of the disadvantages of the prior-art innersoles and methods.